The present invention relates to improvements in oral care compositions, and more particularly relates to a composition for enhancing the effects of tooth whitening compositions.
In the state of the art of oral care compositions and the delivery of such compositions to the site of use in the oral cavity, many means and methods have been utilized and yet numerous issues remain. For an effective ingredient of an oral care composition to have a therapeutic effect, whether for oral cleaning, treatment, or tooth whitening, the effective ingredient must reach and maintain effective contact with the oral care feature long enough to provide its intended effect. Thus, dispersion and penetration into and between the surfaces of various oral features such as the odd shapes of the nooks and crannies of adjacent teeth is a continual issue. So too then is the dwell or contact time necessary or at least preferred for having the effective ingredient or ingredients of an oral care composition maintained in contact with or otherwise disposed adjacent the surface of the oral feature being eared for. Such issues arise in various oral cleaning, treatment and/or tooth whitening situations.
In tooth cleaning and/or treatment, effective ingredients such as fluoride or an anti-gingival agent, e.g., triclosan, must reach the areas between teeth or between a tooth and gums and/or reach the nooks and crannies on/of teeth to provide their benefits to those oral features. Similar activities are necessary in tooth whitening as well. In considering tooth whitening generally, it may first be noted that a tooth is comprised of an inner dentin layer and an outer hard enamel layer that is the protective layer of the tooth. The enamel layer of a tooth is naturally an opaque white or slightly off-white color. It is this enamel layer that can become stained or discolored. The enamel layer of a tooth is composed of hydroxyapatite mineral crystals that create a somewhat porous surface. It is believed that this porous nature of the enamel layer is what allows staining agents and discoloring substances to permeate the enamel and discolor the tooth.
Many substances that a person ingests on a daily basis can “stain” or reduce the “whiteness” of one's teeth. In particular, foods, tobacco products, and fluids such as tea and coffee that one consumes tend to stain one's teeth. These products or substances tend to accumulate on the enamel layer of the teeth and form a pellicle film on the teeth. These staining and discoloring substances can then permeate the enamel layer. This problem occurs gradually over many years, but imparts a noticeable discoloration of the enamel of one's teeth.
Many different oral compositions for stain removal or tooth whitening are available to consumers and dentists for home and professional in-office use. Many of these compositions contain 1-45% by weight concentrations of a peroxygen compound such as hydrogen peroxide and, when applied on the teeth, may effect whitening of stains. These compositions all require different amounts of time to achieve a desired tooth bleaching effect. These times range from 90 to 120 minutes for a dentist-applied, light-activated bleaching system to two weeks or more of overnight exposure for consumer-applied, tray-delivered whitening products. Currently, even the top selling brands of dentist-applied, light-activated, chair-side tooth whitening systems require a minimum of three (3) twenty-minute applications and an overall minimum of ninety (90) minutes or more to complete when all manufacturers' instructions are followed,
Among the chemical strategies available for removing or bleaching tooth stains, the most effective compositions contain an oxidizing agent, usually a peroxygen compound such as hydrogen peroxide, in order to attack the chromogen molecules forming the stains in such a way as to render them colorless, water-soluble, or both. In one of the most popular approaches to whitening a patient's teeth, a dental professional will construct a custom-made, tooth-bleaching tray for the patient from an impression made of the patient's dentition. A prescription oxidizing gel is dispensed into the room-bleaching tray and worn intermittently over a period of time ranging from about 2 weeks to about 6 months, depending upon the severity of tooth staining. These oxidizing compositions, usually packaged in small plastic syringes are dispensed directly by the patient into the custom-made, tooth-bleaching tray and are held in place in the mouth for typical contact times of greater than about 60 minutes, and sometimes as long as 8 to 12 hours. The slow rate of bleaching is in large part due to the nature of the formulations developed to maintain stability of the oxidizing composition.
Alternatively, some oxidizing compositions with relatively high concentrations of oxidizers are applied directly to the tooth surface of a patient in a dental office setting under the supervision of a dentist or dental hygienist. Supervision of application is required with the high concentration oxidizers because of the potential for damage to gums and other oral tissue from the misapplication of highly concentrated oxidizers. Theoretically, such tooth whitening strategies have the advantage of yielding faster results and better overall patient satisfaction.
Oral compositions for whitening teeth are also available containing peracetic acid dissolved or suspended in a vehicle. The peracetic acid may be generated within a dentifrice vehicle by combining water, acetylsalicylic acid, and a water soluble alkali metal percarbonate. Formulatsons for oxygen liberating compositions for the whitening of teeth also use either anhydrous and/or hydrated pastes or gels. Hydrated examples include an aqueous oral gel composition comprising about 0.5% to about 10% by weight urea peroxide and 0.01% to 2% by weight of a fluoride compound, and/or a water containing a hydrogen peroxide-Pluronic thickened oral gel composition. Other examples of whitening or stain removal compounds include toothpastes containing a combination of calcium peroxide and sodium perborate oxidising agents, dicalcium phosphate, calcium carbonate and magnesium carbonate cleaning agents, sorbitol humectant, cornstarch and cellulose gum thickening agents, and an anionic detergent. Oral compositions containing peroxyacids and alkyl diperoxy acids having alkylene groups containing 5-11 carbon atoms are also used for removing stains from teeth.
Another conventional whitening technique is the administration of a light-activated gel under the supervision of a dentist using a protocol of a usual three (3) twenty minute applications. However, patients frequently become uncomfortable, agitated, and/or bored during such a procedure, which typically lasts between 1½ to 2 hours when all set-up and precautionary methods are included. Also, because of the length of exposure to both the gel and the light, teeth and oral tissues can become irritated or experience a transient hypersensitivity reaction. Thus, any improvement that results in decreased exposure time, increased patient comfort and increase in bleaching efficiency is desirable.
In one variation, light or photo-activation implementations have also been developed for use alone or in incorporation with the peroxygen compounds. Here, many kinds of ultraviolet (UV) photo-activators have been identified that naturally reduce the color of chromophoric stains. Exemplary photo-activators include transition metal complexes, keto acids, riboflavin, pteridines, algal pigments, cyanocobalamine, thiamin, biotin, and aromatic ketones. Photo-beaching of tooth surfaces theoretically occurs via one of two pathways. First, the substrate may undergo photoreaction directly if the absorption spectrum of the colored chromagen overlaps with the spectrum of incoming radiation (i.e., the color of the stain fades with exposure to light). Second, UV energy may be absorbed by photo-activators that then chemically react with tooth surface chromagens resulting in an “indirect” photo-bleaching. This is likely a more powerful means for effecting color changes. Indirect photo-bleaching may be mediated by transient species (free radicals) that are rapidly consumed by subsequent reactions. For these mechanisms, the rate of reaction is determined by the quantities and types of chromagens, activators, free radicals, and incoming UV radiation. Surface gradients involving any of these factors will lead to altered rates of photo-bleaching at the enamel/bleaching agent interface.
In nature, the major photochemical intermediate free radicals include singlet oxygen (IO2); superoxide (O2—), hydroperoxide (HO2), and various other peroxy radicals, (RO2). These have been described in a large number of publications including a number of patents for the purpose of bleaching teeth. Singlet oxygen free radicals, 1O2 (the most common type of free radical liberated from hydrogen peroxide (H2O2) in the presence of light, heat, or most activators), are formed primarily through energy transfer from the excited triplet states of dioxygen, 3O2 (as seen in the case of hydrogen peroxide). Wavelengths in the UV-A (315-400 nm) and UV-B (280-315 nm) ranges have been shown to be most effective in their formation. Quantum yields (i.e., the fraction or percentage of absorbed photons which give rise to these free radical products) range from 1% to 3% and generally decrease with increasing wavelength. Because the high concentrations of H2O2 or similar compounds are present in tooth bleaching preparations, the decay of H2O2 into water and 1O2 is prominent when UV light/activator systems are used in professional tooth bleaching formulas.
The exact mechanism of how these singlet oxygen free radicals come to be formed still remains unclear. Some researchers have suggested that 1O2 is formed by direct electron transfer from the excited triplet states to O2. However, reduction of O2 by radicals or radical ions produced by intramolecular electron transfer reactions, H-atom abstractions and/or hemolytic bond cleavages is equally, if not more, plausible. However, it is known that transition metal complexes having single electron reduction potentials falling between the O2/O2— and O2—/H2O2 couples can rapidly catalyze 1O2 free radical formation.
A commercial application has been made of oxidation from the photo-fenton reaction in which reduced metals such as Fe(II) react with H2O2 and UV light to produce a single OH— radical. This may be because hydroxyl moieties may be generated with less UV activation energy reduction in a chromophoric tooth stain in a given period of time or for a given level of UV energy (the high quantum yield for this reaction is 98%).
These extant methods are not quickly or highly effective and indeed need prolonged periods for any minimum effective bleaching effects. These time-consuming methods for teeth whitening thus suggest that any whitening system that can reduce the time factor is desirable.